Using grid resources to execute scientific applications requiring a large amount of computing power is attractive but not easy from the user point of view. Vigne is a grid operating system designed to provide a simplified view of a grid to users. Vigne deals with the very large number of nodes in a large-scale grid and with the nodes' dynamic behavior by using peer-to-peer overlays as a keystone. In this paper, we show why it is highly desirable to use structured and unstructured peer-to-peer overlays for building the high-level services of Vigne grid operating system. To show the interest of our approach, we detail the features of two Vigne services built on top of peer-to-peer overlays. We also present experimental results obtained on the...